The present disclosure relates to a method for determining mechanical damage to a rotor blade of a wind turbine, a computing unit for executing the method, and a correspondingly set up monitoring means.
It is an essential prerequisite for the economic efficiency of wind turbines that, as far as possible, they operate without interruption. In particular, unplanned interruptions of operation due to damage to the drive train or, in particular, to the rotor blades, generate substantial repair costs and frequently result in insurance claims.
To avoid such disadvantages, it is frequently the case with wind turbines that a so-called condition-oriented maintenance is provided, which is effected, for example, on the basis of a vibration-based condition monitoring (CM) of rotor blades in corresponding condition monitoring devices or systems (condition monitoring systems, CMS). Such measures allow early identification of, for example, particular damage in rotor blades. CMS are frequently set up for remote diagnosis, wherein the condition messages are evaluated in certified diagnostic centers, frequently by specially trained personnel.
The use of CMS makes it possible to identify faults at an early stage, avoid unplanned downtimes and reduce costs for stocking of reserve parts, maintenance and production failures. Overall, the availability and production stability are increased as a result.
Known from DE 100 65 314 B4 and WO 2006/012827 A1, for monitoring the condition of rotor blades, are methods and devices in which a structure-borne sound is measured by means of one or more movement sensors disposed on the rotor blades, a frequency spectrum is determined from corresponding signals, by means of appropriate methods, in an evaluation unit, the frequency spectrum is compared with the reference spectra, stored in the evaluation unit, that correspond to defined damage states and special states, and the condition of the rotor blades is determined therefrom. As a result of this, it is intended, inter alia, that the occurrence of localized internal and external damage, and special states of the rotor blades that cause damage, for example extraordinary load situations, can be identified and assessed at an early stage, in order that the operation of the wind turbine can be influenced, preferably in an automated manner. WO 2007/131489 discloses an evaluation of corresponding sensor signals over time, and division of damage events into damage classes.
These methods are found to be insufficient, however, in particular for early identification of lightning damage. There is therefore a requirement for a more reliable prediction and/or identification of corresponding damage.